A hybrid electric vehicle (HEV) is a vehicle which has a driving system consisting of two or more single driving systems able to operate at the same time, in which a driving power of the vehicle is provided by the single driving systems solely or collectively according to an actual driving state of the vehicle. Due to differences of various components, arrangement manners of the various components and control strategies, there results in a plurality of kinds of driving systems. The energy conservation and low emission of the hybrid electric vehicle have gotten a lot of attention in the automobile industry, and have been the focuses of corresponding searches and developments.
In order to keep a good state of the driving hybrid electric vehicle, it is required for the hybrid electric vehicle to shift the gear. Currently, a shift schedule of two parameters (an accelerator and a speed of the vehicle) and a shift schedule of three parameters (an accelerator, a speed of the vehicle and an accelerated velocity) are widely used. However, the shift schedules of two parameters and three parameters are based on the conventional vehicle only having an engine, and are not suitable for the hybrid electric vehicle having double power sources (the engine and the motor). In addition, there may be some problems like big difficulty, poor energy efficiency. etc. in related art for controlling the hybrid electric vehicle.